The type (and only) specimen of Atrociraptor, holotype RTMP 95.166.1, was discovered by Wayne Marshall in 1995, in layers of the Horseshoe Canyon Formation also containing an Albertosaurus bonebed, near Drumheller. This bonebed is located at the top of Unit 4 of the Horseshoe Canyon Formation, which dates to about 68.5 million years ago. The only known specimen consists of parts of the upper and lower jaws—both premaxillae, a right maxilla, both dentaries—teeth and numerous small fragments. The skull appears to have been unusually short and tall. The teeth are relatively straight, but they emerge from the tooth sockets at an angle to the jaw line, resulting in a strongly raked row of teeth. A number of isolated teeth (previously referred to Saurornitholestes) have also been recovered from the Horseshoe Canyon Formation; they can be recognized by their unusually large serrations. [CREDIT: WIKIPEDIA]